Circuit for transmitting high-frequency electric oscillations



M. J. o. STRUTT ETAL' GIRCUIT vFOR TRANSMITTING HIGH-FREQUENCY ELECTRIC os G'ILLATIONS v y Filed Nov. l5, 1946 OUTPUT Patented Aug. 17, 1948 GIRCUIT FOR TEANSMITTING HIGH-FRE'- QUIEN-(375r ELECTRIC OSCILLATIONS.

Maiiiiniliaan JuliiiaOito Stiiiii and. Alfieri van ,der Ziel Eindhoven, Netherlandsi assignors to Hartfor National Bank and Trust Company.

Hartford; Conn, astrustee ApplioationNoyemher 15, 1946', Serial No. 7.313572 1;.n the Netherlands January 13, um

section 1, Public Law 69.9, August s, 19.4.6; Patent' .expires J miliari' 13,196.1'

This invention relates to a circuit for generating high-f'requency-eiectric oscillations with the aid' of' a discharge tube whichl comprises an in put electrode of adjustable biasing potential and vv-hose input oircuit'includfes an oscil'liatoryi circuit tuned to` the frequency oix the oso-illationsfto be generated; f' V"It is known thata circuit 1ofthis kind I-functions diilculty ii the frequencyoi' thoosoil-'lations tobe generated is= so high'thatonehas to reckon with the transit time caf-'the electrons inthe tube. .It the transit time-is appreciable-oom.- pared wit-inthe period of.' the oscillations, then the inputv capacite` ofv the` discharge` tube varies with the biasingvpotentiali of theuinput electrode. Hence, in the case. ofzavariation ofthe. biasing potentialfthe-tunin-gr oftheinput circuit` is also varied. Moreover, atfthosehigh freqlliriiesa virtual ohmoresistance occurs bet-Ween the iiiput electrode and the cathode, the reciprocal valueoi said resistance being usually reterred to. as electronic. damping; and beine alsavariabie with. the. bias-ineuotential o f. the innut electrode. QQnScauentiy, the damniiiaoi the input circuit isa1so...a13i,ed.\ritn a variation of iiieibiasiiig. Diiiills.

itis to eliminate the aboviieiiaied desirable variations- Qi itis. input.- Qerasiii. of. vthe tube by including an ohmic resistance which not shortfciiciiiteii formel1-frequency. in that han `@i the.. cathode lead which is. common to. the inout and the output circuits. The alternating. entrent of. the. cathode biiuesabciit a voltage across. thesaid resistance, which is at. least slib-f stantialiy iii. phase witligtheiilput alternating. vol-tage. impressed upon. the. input electrode.. and. whose. value is. variable with the. siepe of' the.. tube. Characteristic end hence with the biasing. Poteritial. of .iheinpui electrode. across the. resistance. causes iii turn a current fromihe cathode. 'io' the input electrode iii-meh the. natural. Capacity between these two electrodes, which'current is also variable withthe biasing' potential ofithe input electrode and leads; by about 99jL relatively to the input altomai-,ing`

voltage. This current may be considered asy a result of a negative capacity which apparently exists between the input electrode-and the cathode andl whose value is variable with the biasing: potential off the input electrode, saicliv capacity, it it has the correct value, neutralizingthe undosira-ble variations of the input capacity. .Y

The above-.stated undesirable. clampingvariasV tions may also be...eliminated;A asiswell 1m-own,-A by' providing an resistance which is not short-o Thevoliage piQd'uCed;

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circuited for hi-ghpfrequency, in that part ofthe cathode lead which iscommon to the input and the output circuits. For this purpose the ohinic resistance must generally have a higherval/ue than that necessary for compensating thebapacity variations. The elimination ofjthe danilo; ingl variations is, however, `facilitated by -`c n; necting a capacity in parallelv withthe ohh i resistance, the impedance of this capacityvf'rthe frequencies to. @transmitted beine'. ai icf the orderA of'magnit-ud'e ofu the ohmic resistance,4 When a suitable'paraliel capaoityvs use A even possible to eliminatesimultaneously the une desirable capacity variations and the 'darrxp variations;

When oscillations off-high and'very highre quencies are to be generated, a practice hfreto'f fore adopted has beer-itc use a sof-called suctiongridftube; that is, a vdischarge tube compris g' at least one auxiliary' electrode serving asfa tion gridor space-charge grid disposedbetween the-input electrode and theA cathode, and lieingl;V` positively biased withrespect to the catltiorle.V has nowA been found* thaty ina suction-grid tu @L the above-described method olis'eliminating va v" tions of the input capacity and' of the input @rimini-iv with @variation di the. biasing' piiitiitial of the input electrode does not leadptothe desired resultv for the riesen. that. these' variations are of opposingsense relative to the varia.- tions which occur in a tube, having no suction grid. When the suction grid is omitted; the'iriput capacity and: 'the input damping incitan. casete: ingl as the biasing vpotenti-al ofthe input elec# trodfe becomes-less negative- Butin a'suctiongrid tube a decrease ofthe input-capacity and' oi the input dampingJ taires place in the region oi? biasing potentials in which the tube'is generally used. f v According to the'invention, in a circuiticoma prising a suction-grid tube on! elimination o-r crease ofv the variations ofthe input capacity and the input damping inthe casefof a variation of the. biasing potentialiof the inputfelectrodeis obtained b-y introducing an ohmi-c resistaneei-nto the pat-h of highfrequency currents between thek reference to the accompanying drawings, inV

which, Figs. l, 2, and 3 show by way of example certain typical embodiments the diierentiating features of which will also be explained.

Fig. 1 shows a discharge tube I containing a cathode 2, a suction grid 3, an input electrode (control grid) 4 and an output electrodeianode) 5. A resonant input circuit 6 tuned to the frequency of the oscillations to be generated is, on the one hand, connected to the control grid 4' and, on the other hand, coupled via a separating condenser 'l to the cathode 2. Across aresistance 8 the control grid has suppliedto` it a vari-A able biasing potential which may begenerated produces in turn a current via the condenser I to the control grid, which current lags by about 90 relatively to -the alternatingA voltage of the control grid. This current may be regarded as a 4result of a capacity which apparently exists between the control grid and the suction grid and Lwhose value is variable with the biasing potential of the control-grid. Said capacity, if it has the correct value, compensates at least partly for 1 undesirable variations of the input capacity. The compensatingv current flowing to the input electrode contains also a component which is in 'ann-phase with the alternating voltage of the control grid and which, if it has the correct value,

for example in known manner by a regulating rectier for automatic volume control.

The suctiongrid 3 is coupled for high frequency currents via a separating condenser 9 to the cathode, while across a resistance i@ a positive biasing potential is supplied to the suction grid.

The resonant output circuit II is on the one hand connected tothe anode 5 and on the other hand coupled via a separating condenser- I2 to thecathode 2, while the direct voltage of the anode is supplied via a resistance I 3.

In order that variations .of :the input capacity and/or of the input damping with a variation of the control-grid biasing potential may at least partly be eliminated, the alternating current path of the output circuit includes a resistor I4 which is connected to the cathode 2. This connection is 'coupled for high frequency currents across condenser 9 to the suction grid 3 and across condenser I to that extremity of the resonant input circuit 6 which is remote from the control grid. The other extremity of resistor I4 is coupled vla av condenser I5 to the input electrode 4. The resistor I4 as shown in Fig. 1 is devoid of any shunting capacitor vsuch as would be conventionally used, and, accordingly, there is no eiective short circuit for high frequency currents between the suction grid 3 and theresonant circuit ;I,I,

.The operation of the circuit may be explained as follows:

The suction grid 3 has a constant potential. A substantially constant direct current passes out ofthe cathode and iiows partly to the suction grid 3 and for the remaining part to the anode 5. The current distribution between the suction grid and thev anode is controlled by the voltage active on thecontrol grid-4. When the control grid becomes more positive a greater part of the cathode `current. ows to .the anode 5 and when the control grid becomes more negative a' greater part of the cathode current flows to the suction grid 4. Consequently, if an alternating voltage is active on the control grid 4, an alternating current flows from the suction grid through the output circuit to the anode. For alternating currents of the-frequency to be transmitted the suction grid consequently performs the function which in tubes without suction grid is fulfilled bythe cathode.

Thealternating current flowing from the suction grid to the cathode brings about a voltage drop across the resistance I4, which is in phase with the alternating voltage of the controlgrid and whose value is variable with the mutual conductance of the'tube, and hence with the biasing potential. oi the controlgrid. This voltage dropv may at least partly eliminate the variations of .the input damping. To attain this object it is -advantag'eous to connect a condenser in parallel with theA resistance I4, of which condenser the impedance for the oscillations to be generated is at least of the order of magnitude of the resistance I4. f y

In Fig. 2 this parallelcondenser is indicated by I6. The circuit of Fig. 2 differs moreover from that of Fig. 1 in that the tube, in addition to the electrodes already mentioned, contains a screen grid I1 which isvlocated between thev control grid and the anode and which has a positive biasing potential supplied to it via a resistance I8. The function Vof the condenser I5 in the circuit of Fig. 1 is fullled injthe circuit of Fig. 2 by the natural screen grid-control grid capacity, for which purpose the screen grid is connected for high-frequency currents vla a separating condenser I9 to that extremity of the resistance I4 which is remote from the suction grid.

Suction-grid tubes frequently involve the drawback that the natural inductance of that part of the supply conductor for the suction grid which is common to the input and the output circuits causes an undesirable coupling between the inputl and the output circuits, which coupling results in damping -of the input circuit. It has previously been suggested toV eliminate thisv drawback by providing the suction grid with two separate supply conductors and connecting the suction grid for high-frequency currents via one oithese supply conductors to the input circuit and via the other to the output circuit.` l

Fig. 3 shows how the invention can be used in a tube whose suction grid is provided with ltwo supply conductors.` In the circuit of Fig. 3 the suction grid leadl 2,0 is coupled across capacitor 9 to the cathode land thence across capacitor 'I to that extremity of the input circuit 6 .which is remote from the control grid. The conductor 2i connects the suction grid 3 to a resistor III for supply thereto of a positive directcurrent potential.. Conductor 2l also connects the suction grid 4through an alternating current path to the resonant output circuit II, This path includes resistor I4 shunted by capacitor IB and also the blocking capacitor I2, The value of capacitor I6 is so chosen as to oier a high impedance to .the high frequency currents generated. For the rest, .the circuit fully corresponds to that of Fig. 2.

In the circuits of Figs. 2 and 3 it is possibleto give the resistance I4 and the parallel condenser I E such values that the input capacity as well as the input damping are at least substantially invariable with the biasing potential ofthe control grid. The value of the resistance I4 required therefor is generallyfcomprised between 50 and 500 ohms, whileA thev condenser I6. maybe, for

1. A high frequency oscillator circuit arrangement comprising an electron discharge tube having arranged in succession` a cathode, a space chargeelectrode otherwise termed a suction grid, aqcontrol grid and an anode, an oscillatory circuit tuned to the frequency of the oscillations to be generated and coupled between said control grid and cathode, an output circuit coupled betweensaid anode and cathode and comprising a parallel tuned resonant circuit having one terminal thereof coupled to the anode and ohrnic resistor means coupled in series with said resonant circuit and having the free end thereof coupled for radio frequencies -to said base charge electrode, and means to apply to said control grid potential variations occurring at the interconnection between said resonant circuit and said resistor means whereby a feedback potential having an oscillation-sustaining phase relationship with respect to the voltage of said oscillatory circuit is applied to said control grid.

2. A high frequency oscillator circuit arrangement comprising an electron discharge tube having arranged in succession a cathode, a Space charge electrode otherwise termed a suction grid,

a control grid and an anode, an oscillatory circuit tuned to the frequency of the oscillations to be generated and coupled between said control grid and cathode, an output circuit coupled between said anode and cathode and comprising a parallel tuned resonant circuit having one terminal thereof coupled to the anode and ohmic resistor means coupled in series with said resonant circuit and having the free end thereof coupled for radio frequencies to said space charge electrode, and means to capacitatively couple said control grid to the interconnection between said resonant circuit and said resistor means whereby a feedback potential having an oscillation-sustaining phase relationship with respect to the voltage of said oscillatory circuit is applied to said control grid.

3. A high frequency oscillator circuit arrangement comprising an electron discharge tube having arranged in succession a cathode, a space charge electrode otherwise termed a suction grid, a control grid and an anode, an oscillatory circuit tuned to the frequency of the oscillations to be generated and coupled between said control grid and cathode, an output circuit coupled between said anode and cathode and comprising a parallel tuned resonant circuit having one terminal thereof coupled to the anode and ohmic resistor means coupled in series with said resonant circuit and having the free end thereof coupled for radio frequencies to said space charge electrode, a capacitor connector in parallel with said resistor means and having an impedance at the frequency of the oscillations to be generated of the order of magnitude of that of said resistor, and means to capacitively couple said -control grid to 6 thea-interconnection'.between said resonant. circuit and said resistor means wherebya feedback potential having an oscillation-sustainingphase relationship with-respect to the voltage; of said oscillatory-circuit is applied to said control grid.

4.- A- high Afrequency oscillator circuit arrangement comprising an electron discharge tube havingy arrangedV in succession ya cathode, a space Charge velectrode otherwise termed a suction grid, .a controlA grid and an anode, an oscillatory circuit tuned tothe frequency of the -oscillations to begenerated andcoupled between said control -gridiandcathoda an output circuit coupled between said anode and cathode and comprising` a parallelltuned resonant circuit having one terminal thereof coupled to the anode and` ohmic resistor'means coupled in series withsaid resonant circuit and having the free end thereof coupled i'or radio frequencies to Asaid space charge elec,.- trode, and means comprising a capacitor to couple saidfcontrol grid tothe interconnection between said resonant circuit and said resistor means kwhereby a feedback potential havingk an'oscillation-sustaining phase relationship with respect to the voltage of said oscillatory circuit is applied to said control grid.

5. A high frequency oscillator circuit arrangement comprising an electron discharge tube having arranged in succession a cathode, a space charge electrode otherwise termed a suction grid, a control grid and an anode, an oscillatory circuit tuned to the frequency of the oscillations to be generated and coupled between said control grid and cathode, an output circuit coupled between said anode and cathode and comprising a parallel tuned resonant circuit having one terminal thereof coupled tothe anode and ohmic resistor means coupled in series with said resonant circuit and having the free end thereof coupled for radio frequencies to said space charge electrode, and means comprising a screening grid electrode interposed between said control grid and said anode and in capacitive relationship with said control grid to capacitively couple said control grid to the interconnection between said resonant circuit and said resistor means whereby a feedback potential having an oscillation-sustaining phase relationship with respect to the voltage of said oscillatory circuit is applied to said control grid.

6. A high frequency oscillator circuit arrangement comprising an electron discharge tube having arranged in succession a cathode, a space charge electrode otherwise termed a suction grid, a control grid and an anode, an oscillatory circuit tuned to the frequency of the oscillations to be generated and coupled between said control grid and cathode, an output circuit coupled between said anode and cathode'and comprising a parallel tuned resonant circuit having one terminal thereof coupled to the anode and ohmic resistor means coupled in series with said resonant circuit and having the free end thereof connected to said cathode and capacitively coupled for radio frequencies to said space charge electrode, a capacitor connected in parallel with said resistor means and having an impedance value at the frequency to be generated of the order of magnitude of that of said resistor means, and means comprising a screening grid electrode interposed between said control grid and said anode and in capacitive relationship with said control grid to apply to said control grid potential variations occurring at the interconnection between said resonant circuit and said resistor means whereby a feedback potential lhavingl lan oscillation-sustaining phase relationship with respect to the voltage of said oscillatory circuit-is applied to said control grid.

7. A high frequency oscillator circuit arrangement comprising an electron dischargeftube having arranged in succession `a cathode, a space chargeelectrode otherwise termed a suction grid, a control grid and an anode, an oscillatory circuit tuned to the frequency of the oscillations t0 be generated and coupled between said control grid `and cathode, an output circuit coupled between said anode and cathode and comprising a parallel tuned resonant circuit having one terminal thereoi coupled to the anode and ohmic resistor means coupled in series with said resonant circuit and having the free end thereof capacitively coupled for radio frequencies to said cathode and connected to said space charge electrode, a capacitor connected in parallel with said resistor means and having an impedance value at the frequency to he generated of the order-of magnitude of that of said resistor means, and means comprising a Yscreening grid electrode interposed between said 8 control'grid and said anode `and'in capacitive relationship with said control grid to apply to said control grid potential variations occurring at vthe interconnection between said resonant circuit and said resistor means whereby a feedback potential having an osciliation-sustaining phase relationship with respect to the Voltage of said oscillator circuit is applied to said control grid.

MAinMImAAN JULIUs o'rrro sTRUT'r, i ALBERT VAN DER ZIEL.

` REFERENCES CITED The following references are of record in the le of this patent: V

UNITED STATES PATENTS 

